Negative pressure updraught pouring device and method

ABSTRACT

A negative pressure updraught pouring device and method are provided. A melting furnace has a top end covered by a flat plate with a suction pipe that has a bottom end dipped into the molten steel in the melting furnace. A mold is placed on the flat plate and the mold&#39;s flow path system is connected with the suction pipe. A chamber is covered on the mold and the flat plate, and the air inside the chamber is drawn out to reduce the air pressure inside the chamber and the mold cavity. When the mold cavity is filled with molten steel, a driving assembly is used to move a blocker to substantially block the flow of the molten steel in the flow path system. The negative air pressure is relieved to flow the molten steel inside the flow path system back into the melting furnace.

CROSS-REFERENCE TO RELATED DOCUMENTS

The present invention is a continuation in part (CIP) to a U.S. patent application Ser. No. 14/626,667 entitled “Negative Pressure Updraught Pouring Method” filed on 2015 Feb. 19.

BACKGROUND OF THE INVENTION Field of Invention

The present invention relates to a pouring device and method, and more particularly, to a negative pressure updraught pouring device and method used for draughting molten steel upwards into a mold to form a cast by negative pressure.

Description of the Related Art

Referring to FIG. 5, the Gravity pouring method employed by conventional iron and steel foundry plants mainly comprises steps of: after steel is fused to 1450˜1700° C. by a melting furnace, the high temperature molten steel is filled in an iron bucket (d) and then the molten steel is poured and casted into a pre-manufactured mold (a); the molten steel is poured into a mold cavity c through a pouring basin (b1), a vertical sprue (b2), a runner (b3) and a gate (b4) of a flow path system (b) by gravitational effect; and the cooled and solidified molten steel is taken out from the mold (a). The solidified molten steel is cleaned and processed properly for obtaining a cast required.

The above pouring method is mainly used in iron and steel foundry. Nevertheless, the pouring method has the following drawbacks based on the foundry costs and quality of casts:

1. For casts with a thickness below 3.5 mm, the molten steel is required for passing through the flow path system when it is casted into the sand mold by gravitational effect. Flowing speed of the molten steel is not too fast due to the obstruction of the air in the mold cavity. The thinner is the thickness of the cast; the slower is the flowing speed. The longer is the flowing path; the faster is the quenching speed of the molten steel. Therefore, the thin thickness of the cast is hard to form if the temperature of the molten steel is not high and the flowability is poor. As a result, it is difficult to obtain casts with good quality.

2. When the melting temperature reaches 1700° C. or higher, even though the flowability of the molten steel can be increased for forming casts with a thin thickness, but not only that the electricity consumption is increased, the lifespan of refractory materials of the melting furnace is shortened substantially after the melting temperature is increased. The frequency for changing the refractory materials has to increase which will increase the costs for changing the refractory materials and reduce the production capacity due to the downtime for changing. Furthermore, when the melting temperature of the molten steel is over 1700° C., the refractory materials of the melting furnace will be fused with the molten steel. As a result, the amount of oxide-containing impurities in the molten steel increases which will affect the purity and mechanical property of the steel casts.

During the pouring process, the molten steel is required to fill up the flow path system including the pouring basin, the vertical sprue and the runner for flowing into the mold cavity. The molten steel inside the flow path system and that inside the mold cavity will be cooled down and solidified at the same time. The molten steel retaining inside the flow path system will increase the consumption of molten steel. As a result, the ratio (i.e. yield) of the amount of casts and that of the total pouring molten steel cannot be enhanced effectively. The ineffectiveness of enhancing the yield means the amount of molten steel cannot be saved effectively, the energy source cannot be saved effectively and thus the production costs cannot be reduced effectively.

SUMMARY OF THE INVENTION

In view of the above, a negative pressure updraught pouring method of the present invention is provided for improving the afore-mentioned drawbacks of the conventional structures and achieving the following objectives.

A primary objective of the present invention is to provide a negative pressure updraught pouring method for solving the problem of difficulty in forming casts with a thin thickness when the molten steel temperature is not high and meeting the requirements of casts with a thin thickness.

Another objective of the present invention is to provide a negative pressure updraught pouring method for solving the drawback of the high molten steel temperature in order that the power consumption can be reduced, the loss and changing frequency of refractory materials can be reduced, the purity and mechanical property of casts can be enhanced and thus the production costs can be reduced.

Another objective of the present invention is to provide a negative pressure updraught pouring method for solving the drawback of redundant molten steel remaining inside the flow path system which causes the ineffectiveness of enhancing the yield ratio in order that the costs for reclaiming the molten steel can be saved and the output can be increased effectively.

Another objective of the present invention is to provide a negative pressure updraught pouring method for solving the drawback of the requirement of using the iron bucket for pouring. The iron bucket and related equipment are no longer needed and thus the production costs can be reduced.

Another objective of the present invention is to provide a negative pressure updraught pouring device and method for allowing the molten steel rapidly and in a large amount to flow into the cavity and for substantially blocking the flow of the molten steel in the flow path system by using a blocker.

In order to achieve the above-mentioned objectives, the present invention provides a negative pressure updraught pouring device for a plurality of molds to form a plurality of casts, where each mold has a mold cavity, a flow path system, and an air passage, the mold cavity and the flow path system are connected with each other inside the mold while the air passage is connected with the mold cavity, and each mold is a sand mold and its air passage on the mold is a gap between sand grains of the sand mold; a flat plate having a suction pipe is covered onto a top end of a melting furnace; the mold is placed on the flat plate, and the flow path system of the mold is connected with a top end of the suction pipe; a chamber is connected with an extraction device and is placed over the mold and the flat plate to draw the air inside the chamber out; the negative pressure updraught pouring device is characterized in that: a blocker is provided within the mold, where the blocker has one end provided with a driving assembly for driving the blocker so as to move another end of the blocker to block substantially the flow path system in the mold.

In implementation, the flow path system includes a main flow path and at least one in-flow path, the main flow path is connected with the top end of the suction pipe, while the at least one in-flow path is located between the main path and the mold cavity; the another end of the blocker is connected into the at least one in-flow path.

In implementation, the mold is provided with a connecting tude therein, the connecting tube is connected into the main flow path, and the connecting tube has a top end in communication with the in-flow path and has a bottom end in communication with the top end of the suction pipe.

In implementation, the mold includes a upper die and a lower die, the upper die has a bottom surface provided with a bowl-shaped recess, the bowl-shaped recess has a top end from which a vertical hole is extended upwardly, and the vertical hole is upwardly in communication with a space outside the upper die; the another end of the blocker is provided with a bowl-shaped portion with an opening that faces downwardly, for being positioned into the bowl-shaped recess; and the driving assembly includes a pushing rod and a driving element that are moved in a linkage way, and the pushing rod has one end located within the vertical hole for pushing the blocker to be moved downwardly. In one embodiment, one end of the blocker is a standing pillar for positioned within the vertical hold.

In implementation, one end of the pushing rod is in a separate and disconnecting state with the blocker.

In implementation, the negative pressure updraught pouring device further comprises at least two pressing-plate assemblies, where each pressing-plate assembly includes a pressing plate and a pushing element, the pressing plate is located within the chamber, and the pushing element has one end connected with the pressing plate, so as to move the pressing plate downwardly to be positioned.

The present invention also provides a method using the negative pressure updraught pouring device as mentioned above, comprising steps of: a. covering the top end of the melting furnace with the flat plate having the suction pipe, filling the melting furnace with molten steel, and dipping a bottom end of the suction pipe into the molten steel; b. placing the mold on the flat plate to connect the flow path system of the mold with the top end of the suction pipe, and placing the chamber over the mold and the flat plate, drawing the air inside the chamber out to reduce the air pressure inside the chamber and the mold cavity, so as to suck the molten steel inside the melting furnace upwardly through the suction pipe to flow the molten steel into the mold cavity; c. when the mold cavity is filled with the molten steel, using the driving assembly to drive the blocker, so as to move the another end of the blocker to block substantially the flow path system in the mold; then relieving the negative air pressure inside the chamber to flow the molten steel inside the flow path system back into the melting furnace; d. removing the chamber and the driving assembly, and moving the mold and the blocker, while keeping the flat plate unmoved to cover the top end of the melting furnace; and e. repeating the steps b to d until the treatment of the plurality of molds is completed.

In implementation, in step b, when the chamber is placed over the mold and the flat plate, using at least one pushing element to push at least one pressing plate, so as to move the at least one pressing plate downwardly to be pressed against the mold's top surface to have the mold positioned.

The present invention will become more fully understood by reference to the following detailed description thereof when read in conjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explosive view of elements used with a preferred embodiment of a negative pressure updraught pouring method of the disclosure;

FIG. 2 is a sectional assembly view of the elements used with the preferred embodiment of the negative pressure updraught pouring method of the disclosure;

FIG. 3 is a sectional view of the preferred embodiment of the negative pressure updraught pouring method of the disclosure when a negative pressure is formed;

FIG. 4 is a sectional view of molten steel of the preferred embodiment of the negative pressure updraught pouring method of the disclosure being flowed back into a melting furnace;

FIG. 5 is a sectional view of molten steel being casted into a mold used with a conventional sand mold pouring method;

FIG. 6 is a sectional assembly view of the elements used with the preferred embodiment of the negative pressure updraught pouring device of the disclosure;

FIG. 7 shows the use of the preferred embodiment of the negative pressure updraught pouring device of the disclosure when a negative pressure is formed;

FIG. 8 shows the use of the preferred embodiment of the negative pressure updraught pouring device of the disclosure, where the flow of the molten steel is blocked by using a blocker and the molten steel flow back into the melting furnace; and

FIG. 9 shows the removal of the chamber, the driving assembly, the casted mold, and the blocker from the flat plate when the casting procedure using the preferred embodiment of the disclosure is finished.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Please refer to FIGS. 1 to 4. A preferred embodiment of a negative pressure updraught pouring method of the present invention comprises following steps of:

a) a flat plate 3 with a suction pipe 4 is covered on a top end of a melting furnace 2, the melting furnace 2 is filled with fused molten steel 9, and a bottom end of the suction pipe 4 is dipped into the molten steel 9;

b) an air passage 52 connected with a mold cavity 51 is formed on a mold 5, and the mold 5 is placed on the flat plate 3 in order that a flow path system 53 of the mold 5 is connected with a top end of the suction pipe 4;

c) a chamber 6 is covered on the mold 5 and the flat plate 3, and the air inside the chamber 6 is drawn out to reduce the air pressure inside the chamber 6 and the mold cavity 51, the molten steel 9 inside the melting furnace 2 is sucked upwardly and flowed into the mold cavity 51 through the suction pipe 4 for forming a cast; and

d) solidifying the molten steel within a gate 54 between the flow path system 53 and the mold cavity 51, and then the negative air pressure inside the chamber 6 is relieved so that the molten steel 9 inside the flow path system 53 can be flowed back into the melting furnace 2.

The melting furnace 2 in the step is a coil heating type melting furnace. The melting temperature of the molten steel 9 is controlled between 1400˜1550° C. The suction pipe 4 is penetrated through the flat plate 3 vertically and an opening of the bottom end of the suction pipe 4 is dipped into the molten steel 9. An opening of the top end of the suction pipe 4 and a top surface of the flat plate 3 are roughly on a same plane.

The mold 5 in the step b is a sand mold. The air passage 52 on the mold 5 is a gap between each one of sand grains of the sand mold for creating air permeable effect. An intake 531 of the flow path system 53 of the mold 5 is formed on a bottom surface of the mold 5 in order that the intake 531 can be aligned with the opening of the top end of the suction pipe 4 when the mold 5 is placed on the flat plate 3, and thus the flow path system 53 of the mold 5 can be connected with the top end of the suction pipe 4.

In the step c, the chamber 6 is a hollow container with a bottom opening. A top end of the chamber 6 is connected with an air exhaust tube 61 in order that a vacuum pump is used for extracting air inside the chamber 6 when the chamber 6 is covered on the mold 5 and the flat plate 3. Due to the air permeability of the mold 5, the air pressure inside the chamber 6 is the same as that of the mold cavity 51, the flow path system 53 and the suction pipe 4. Therefore, negative pressure can be used for sucking the molten steel 9 inside the melting furnace 2. The molten steel 9 can flow upward through the suction pipe 4 and then into the mold cavity 51 through the flow path system 53. When the negative pressure updraught pouring method of the present invention is embodied, a plurality of the mold cavity 51 can be disposed for forming a plurality of casts at the same time.

In the step d, after the molten steel 9 has flowed into the mold cavity 51, the molten steel 9 is allowed to stand for a period of time. Then, before the molten steel 9 inside the mold cavity 51 is completely solidified, and the molten steel 9 within the gate 54 between the flow path system 53 and the mold cavity 51 is solidified, the negative air pressure inside the chamber 6 is relieved so that the unsolidified molten steel 9 inside the flow path system 53 can flow back downwardly into the melting furnace 2.

After the molten steel 9 has completely flowed back into the melting furnace 2, remove the chamber 6 and detach the mold 5 from the flat plate 3 in order that the molten steel 9 inside the mold 5 continues to cool down. A new mold 5 can be placed on the flat plate 3 for performing pouring again.

Refer to FIG. 6, it shows the preferred embodiment of the negative pressure updraught pouring device 1′ of the disclosure. The negative pressure updraught pouring device 1′ is used for a plurality of molds to form a plurality of casts and comprises a melting furnace 3′, a flat plate 4′, a mold 2′, a chamber 5′, an extraction device 6′, at least two pressing-plate assemblies 7′, a blocker 8′, and a driving assembly 9′.

The melting furnace 3′ has a top end provided with an opening, and has peripheries provided with coils so as to control the temperature of the molten steel in the melting furnace 3′ to be in the range from 1500 to 1600° C. by heating the coils. In implementation, the molten steel in the melting furnace 3′ also can be heated by other indirect or direct means. The flat plate 4′ is covered upon the opening at the top end of the melting furnace 3′. The flat plate 4′ has a vertically hollow ceramic suction pipe 41′, and the suction pipe 41′ passes through the plate surface of the flat plate 4′ and has an opening at its top end located substantially on the same horizontal level with the plate surface of the flat plate 4′

The mold 2′ is a sand mold and its air passage 21′ on the mold is a gap between sand grains of the sand mold for good air permeability. The mold 2′ includes an upper die 22′ and a lower die 23′. The upper die 22′ has a bottom surface provided with an upwardly-recessed bowl-shaped recess 221′. The bowl-shaped recess 221′ has a top end from which a vertical hole 222′ is extended upwardly. The vertical hole 222′ is upwardly in communication with a space outside the upper die 22′. In this embodiment, the mold 2′ is provided therein with four mold cavities 24′ and a flow path system 25′ that are in communication with each other. The four mold cavities 24′ are in communication with the space outside the mold 2′ via the air passage 21′ of the mold 2′. The flow path system 25′ includes a main flow path 251′ and four in-flow paths 252. The main flow path 251′ is a vertical channel in a round-tube shape and is axially connected with a connecting tube 26′. The connecting tube 26′ has a top end in communication with the four in-flow paths 252′ and the four in-flow paths 252′ are located between the top end of the connecting tube 26′ and the four mold cavities 24′. When the mold 2′ is placed on the plate surface of the flat plate 4′, the connecting tube 26′ has a bottom end in communication with the top end of the suction pipe 41′. In implementation, there could be one group or two groups of the cavities 24′ and the in-flow paths 252′ for one or more than one mold to form casts. The lower die 23′ has a bottom surface provided with a circular leakproof ceramic packing ring 231′.

The chamber 5′ is a hollow container having a bottom surface provided with an opening. The chamber 5′ is placed over the mold 2′ and the flat plate 4′, so as to have the mold 2′ located between the top surface of the flat plate 4′ and the internal walls of the chamber 5′. The chamber 5′ is connected with one end of the extraction tube 51′ and the extraction tube 51′ has another end connected with a vacuum pump. The vacuum pump is used as the extraction device 6′ for drawing out the air in the chamber 5′.

In this embodiment, there are two pressing-plate assemblies 7′, and the two pressing-plate assemblies 7′ are set side by side. Each pressing-plate assembly 7′ includes a pressing plate 71′ and a pushing element 72′. The pressing plate 71′ is vertically movable and located within the chamber 5′. The pressing plate 71′ has a top surface upwardly connected with the bottom of the pushing element 72′. The pushing element 72′ is a cylinder for pushing the pressing plate 71′ downwardly to be positioned. In implementation, the pushing element also can be an oil cylinder or a mechanical structure comprising the combination of a stepper motor and racks for the same purpose of moving the pressing plate 71′ vertically.

The top end of the blocker 8′ is a standing pillar 81′. The standing pillar 81′ is inserted into the vertical hole 222′ of the upper die 22′ and is positioned in the vertical hole 222′. The blocker 8′ has a bottom end provided with a bowl-shaped portion 82′ having an opening that faces downwardly and enclosed peripheries. The external curved peripheries of the bowl-shaped portion 82′ are closely attached onto the external curved peripheries of the bowl-shaped recess 221′ of the upper die 22′, so as to position the bowl-shaped portion 82′. When the blocker 8′ is positioned within the upper die 22, the bottom surface of the bowl-shaped portion 82′ is adjacent to the in-flow path 252′.

The driving assembly 9′ includes a pushing rod 91′ and a driving element 92′ that are moved in a linkage way. The upper part of the pushing rod 91′ is provided with a rack and the pushing rod 91′ has a bottom end passing through the vertical hole 222′ of the upper die 22′ and located in the vertical hole 222′. The bottom end of the pushing rod 91′ is in a separate and disconnecting state with the top end of the blocker 8′. The driving element 92′ is a stepper motor with gears, so that when the stepper motor rotates, the pushing rod 92′ is driven by the gears to move downwardly. Consequently, the standing pillar 81′ of the blocker 8′ is pushed by the bottom end of the pushing rod 91′ to move the blocker 8′ downwardly. In implementation, the driving element 92′ also can be an oil cylinder or a pneumatic cylinder for the same purpose of moving the pushing rod 91′ downwardly.

The present invention also provides a method using the negative pressure updraught pouring device according to the present invention, which comprises steps of: a. covering the top end of the melting furnace 3′ with the flat plate 4′ having the suction pipe 41′, filling the melting furnace 3′ with molten steel, and dipping a bottom end of the suction pipe 41′ into the molten steel; b. as shown in FIG. 7, placing the mold 2′ on the flat plate 4′ to connect the flow path system 25′ of the mold 2′ with the top end of the suction pipe 41′, and placing the chamber 5′ over the mold 2′ and the flat plate 4′, drawing the air inside the chamber 5′ out to reduce the air pressure inside the chamber 5′ and the mold cavity 24′, so as to suck the molten steel inside the melting furnace 3′ upwardly through the suction pipe 41′ to flow the molten steel into the mold cavity 24′; c. as shown in FIG. 8, when the mold cavity 24′ is filled with the molten steel, using the driving assembly 9′ to drive the blocker 8′, so as to move another end of the blocker 8′ to block substantially the flow of the molten steel in the flow path system 25′; then relieving the negative air pressure inside the chamber 5′ to flow the molten steel inside the flow path system 25′ back into the melting furnace 3′; d. as shown in FIG. 9, removing the chamber 5′ and the driving assembly 9′, and moving the mold 2′ and the blocker 8′, while keeping the flat plate 4′ having the suction pipe 41′ unmoved to cover the top end of the melting furnace 3′; and e. repeating the steps b to d until the treatment of the plurality of molds is completed.

When the extraction device 6′ is used to draw out the air within the chamber 5′, because the mold 2′ is air permeable, it is able to reduce the air pressure within the chamber 5′ to have the chamber 5′, mold cavity 24′, flow path system 25′, connecting tube 26′, and suction pipe 41′ under the same air pressure. Consequently, the molten steel in the molten furnace 3′ is drawn upwardly through the suction pipe 41′ and the flow path system 25′ to flow into the mold cavity 24′.

As shown in FIG. 7, in step b, when the chamber 5′ is placed over the mold 2′ and the flat plate 4′, two pushing elements 72′ are used to push the two pressing plates 71′, so as to move the pressing plates 71′ downwardly to be pressed against the top surface of the mold 2′ to position the mold 2′. In this way, the leakage of the molten steel can be prevented. Moreover, since the packing ring 231′ is placed between the bottom surface of the lower die 23′ and the top surface of the flat plate 4′, it is able to prevent the leakage of the molten steel from the gap between the bottom surface of the lower die 23′ and the top surface of the flat plate 4′.

When the mold cavity 24′ is filled with the molten steel, the driving assembly 9′ is used to drive the blocker 8′ to move the blocker 8′ and have the bowl-shaped portion 82′ at the bottom end of the blocker 8′ to cover the top end of the connecting tube 26′, so as to block substantially the communication between the main flow path 251′ and the four in-flow paths 252′. The flow of the molten steel in the flow path system 25′ also can be blocked by covering the four in-flow paths 252′ with the bowl-shaped portion 82′. The flow of the molten steel in the flow path system 25′ is substantially blocked by closely fitting the bottom end of the bowl-shaped portion 82′ with the top end of the connecting tube 26′. It is allowable to have tiny gaps between the bottom end of the bowl-shaped portion 82′ with the top end of the connecting tube 26′, that is, though the flow of the molten steel is almost blocked in the flow path system 25′, extremely small amount of leakage that can be rapidly solidified is allowed.

When the flow of the molten steel in the flow path system 25′ is substantially blocked, the molten steel in the mold cavity 24′ can remain molten or mildly solidified. Now the negative air pressure inside the chamber 5′ is relieved to flow the molten steel inside the flow path system 25′ back into the melting furnace 3′. When the back flow is complete, the chamber 5′, the pressing-plate assemblies 7′, and the driving assembly 9′ are removed while the mold 2′ and the blocker 8′ are detached from the flat plate 4′. After that, a new mold could be placed on the flat plate 4′ to perform the pouring again.

As a conclusion, the negative pressure updraught pouring method of the present invention has the following advantages:

1. The present invention employs negative pressure updraught method to suck the molten steel into the mold cavity. The thickness of the cast can be reduced to below 2.5 mm. Thus, products that demand special requirement of casts with a thin thickness (such as turbochargers).

2. The present invention employs negative pressure updraught method to suck the molten steel into the mold cavity. Even though the molten steel temperature is between 1400˜1550° C., the molten steel can still flow smoothly inside the flow path system. Therefore, the decrease of the melting temperature of the molten steel not only can reduce the power consumption in order to save energy source, the loss of refractory materials fused into the molten steel can be reduced in order that the purity and mechanical property of the cast can be enhanced. As a result, the changing frequency of the refractory materials of the melting furnace can be reduced in order to reduce the production costs.

3. The present invention allows the unsolidified molten steel to flow back into the melting furnace for being used in the next pouring after the present pouring is finished. Therefore, the yield ratio can be enhanced effectively, the costs for reclaiming can be saved and the output can be increased.

4. The present invention employs negative pressure updraught method to suck the molten steel into the mold cavity. Therefore, the melting temperature of the molten steel can be reduced. Furthermore, shorter flow path system can be used. No impurities will be mixed in the molten steel when the unsolidified molten steel flows back into the melting furnace. Consequently, negative effects on the mechanical property of the steel casts caused by impurities can be prevented.

5. The melting furnace of the present invention is a coil heating type melting furnace. Fused molten steel can be provided directly for the sucking of the suction pipe in order that casts can be formed. Therefore, not only that the pouring process is made more simplified and more effective, no iron bucket and related equipment are needed for reducing the production costs.

6. By means of using the blocker to substantially block the flow of the molten steel in the flow path system, the negative air pressure inside the chamber can be relieved when the steel in the mold cavity remains molten or mildly solidified for the molten steel inside the flow path system to flow back into the melting furnace. The mold then can be moved to elsewhere for further solidification. In other words, the mold can be removed before the solidification of the molten steel in the mold cavity is complete, so as to shorten the duration during which the mold is placed on the flat plate.

7. The pushing rod and the blocker are in a separate and disconnecting state and the bowl-shaped portion at the bottom end of the blocker is positioned into the bowl-shaped recess of the upper die according to the present invention. Thereby, when the casting is complete, it is easy to remove both of the chamber and pushing rod and move the mold and the blocker.

8. According to the present invention, the mold can be effectively positioned by using at least one pushing element to push at least one pressing plate, so as to move the at least one pressing plate downwardly to be pressed against the top surface of the mold. Thereby, it is able to prevent the leakage of the molten steel that flows upwardly. Moreover, the use of the pressing-plate assembly makes it easier for the attachment and detachment of the upper die and the lower die with the flat plate.

As a conclusion from the above disclosed descriptions, the expected objectives can be achieved by the negative pressure updraught pouring method of the present invention which not only can allow casts to have a thin thickness, the production costs can be reduced, output can be enhanced, manufacturing process can be simplified, and quality of casts can be ensured.

Although the embodiments of the present invention have been described in detail, many modifications and variations may be made by those skilled in the art from the teachings disclosed hereinabove. Therefore, it should be understood that any modification and variation equivalent to the spirit of the present invention be regarded to fall into the scope defined by the appended claims. 

1. A negative pressure updraught pouring device provided for a plurality of molds to form a plurality of casts, where each mold has a mold cavity, a flow path system, and an air passage, the mold cavity and the flow path system are connected with each other inside the mold while the air passage is connected with the mold cavity, and each mold is a sand mold and its air passage on the mold is a gap between sand grains of the sand mold; a flat plate having a suction pipe is covered onto a top end of a melting furnace; the mold is placed on the flat plate, and the flow path system of the mold is connected with a top end of the suction pipe; a chamber is connected with an extraction device and is placed over the mold and the flat plate to draw the air inside the chamber out; the negative pressure updraught pouring device is characterized in that: a blocker is provided within the mold, where the blocker has one end provided with a driving assembly for driving the blocker so as to move another end of the blocker to block substantially the flow path system in the mold.
 2. The negative pressure updraught pouring device as claimed in claim 1, wherein the flow path system includes a main flow path and at least one in-flow path, the main flow path is connected with the top end of the suction pipe, while the at least one in-flow path is located between the main path and the mold cavity; the another end of the blocker is connected into the at least one in-flow path.
 3. The negative pressure updraught pouring device as claimed in claim 2, wherein the mold is provided with a connecting tube therein, the connecting tube is axially connected into the main flow path, and the connecting tube has a top end in communication with the in-flow path and has a bottom end in communication with the top end of the suction pipe.
 4. The negative pressure updraught pouring device as claimed in claim 1, wherein the mold includes a upper die and a lower die, the upper die has a bottom surface provided with a bowl-shaped recess, the bowl-shaped recess has a top end from which a vertical hole is extended upwardly, and the vertical hole is upwardly in communication with a space outside the upper die; the another end of the blocker is provided with a bowl-shaped portion with an opening that faces downwardly, for being positioned into the bowl-shaped recess; and the driving assembly includes a pushing rod and a driving element that are moved in a linkage way, and the pushing rod has one end located within the vertical hole for pushing the blocker to be moved downwardly.
 5. The negative pressure updraught pouring device as claimed in claim 4, wherein one end of the pushing rod is in a separate and disconnecting state with the blocker.
 6. The negative pressure updraught pouring device as claimed in claim 5, wherein one end of the blocker is a standing pillar for positioned within the vertical hold.
 7. The negative pressure updraught pouring device as claimed in claim 4, wherein one end of the blocker is a standing pillar for positioned within the vertical hold.
 8. The negative pressure updraught pouring device as claimed in claim 1, further comprising at least two pressing-plate assemblies, where each pressing-plate assembly includes a pressing plate and a pushing element, the pressing plate is located within the chamber, and the pushing element has one end connected with the pressing plate, so as to move the pressing plate downwardly to be positioned.
 9. A method using the negative pressure updraught pouring device as claimed in claim 1, comprising steps of: a. covering the top end of the melting furnace with the flat plate having the suction pipe, filling the melting furnace with molten steel, and dipping a bottom end of the suction pipe into the molten steel; b. placing the mold on the flat plate to connect the flow path system of the mold with the top end of the suction pipe, and placing the chamber over the mold and the flat plate, drawing the air inside the chamber out to reduce the air pressure inside the chamber and the mold cavity, so as to suck the molten steel inside the melting furnace upwardly through the suction pipe to flow the molten steel into the mold cavity; c. when the mold cavity is filled with the molten steel, using the driving assembly to drive the blocker, so as to move the another end of the blocker to block substantially the flow path system in the mold; then relieving the negative air pressure inside the chamber to flow the molten steel inside the flow path system back into the melting furnace; d. removing the chamber and the driving assembly, and moving the mold and the blocker, while keeping the flat plate unmoved to cover the top end of the melting furnace; and e. repeating the steps b to d until the treatment of the plurality of molds is completed.
 10. The method as claimed in claim 9, wherein in step b, when the chamber is placed over the mold and the flat plate, using at least one pushing element to push at least one pressing plate, so as to move the at least one pressing plate downwardly to be pressed against the mold's top surface to have the mold positioned. 